This invention relates to a process for the preparation of an insecticide-containing device such as a pet collar for the control of fleas or ticks on warm blooded animals or a pest strip or the like for the control of common houseflies (Musca domestica), fruit flies (Drosphila melanogaster), mosquitoes (Culex pipiens) or the like. In particular, this invention relates to a novel process for the manufacture of a shaped body comprised of a synthetic resin having dispersed therein the insecticide 1,2-dibromo-2,2-dichloroethyl dimethyl phosphate, commonly known as naled, alone or in combination with one or more other insecticides.
Heretofore, insect-combatting devices, such as pet collars, pest strips and the like, comprised of a PVC resin having a dispersion of the insecticide dimethyl 2,2-di-chlorovinyl phosphate, commonly known as DDVP or by its trademark Vapona, have been widely used for the purpose of controlling fleas and flying insects such as houseflies, mosquitoes and the like in the vicinity of the device. However, DDVP has been reported to have an objectionable depressing effect on the plasma and red cell cholinesterase at least in animals which effect is particularly acute at high concentrations which are produced during the first few days after a pest strip has first been exposed to the atmosphere. This is believed due to the fact that the liberation rate of DDVP from presently available DDVP-containing pest strips is not uniform but rather is higher during the first few days after activation, i.e., removal of the pest strip from the packing and exposing it to the atmosphere. There are also indications that DDVP may be harmful to humans. Pest strips containing DDVP have been banned in Holland. Moreover, the aforementioned initial high liberation rate represents an unduly rapid loss of insecticide and creates an upper limit on the period that DDVP is liberated at a rate sufficient to effectively control pests. DDVP also has been found to possess a high degree of residual toxicity in the area of the device, apparently from adsorption of the DDVP vapors in walls, floors, ceilings, curtains, rugs and the like. Even after a DDVP-containing device is removed from a room environment, residual DDVP vapors can often be detected for several days thereafter.
It has also been suggested to utilize other insecticides such as naled (1,2-dibromo-2,2-dichloroethyl dimethyl phosphate) in an insert-combatting device. The preparation of naled is described in U.S. Pat. No. 2,971,882 to Osmonson et al. PVC resin-naled combinations have been proposed for use as an insecticide of a general nature in French Pat. No. 1,568,198, issued Apr. 14, 1969, and in U.S. patent application Ser. No. 85,445, filed Jan. 30, 1961 (abandoned, but accessible to the public), and corresponding British Pat. No. 955,350. Netherlands published application No. 6,610,279 discloses fly strips composed of PVC-naled as well as PVC-DDVP combinations which are stated to have such high insecticide release rates as to require an outer laminate layer to retard the insecticide release. U.S. Pat. No. 3,344,021 discloses PVC-naled combinations for use as an anthelmintic composition.
A number of problems have been encountered in providing a commercially satisfactory PVC resin-naled combination for use in an insect-combatting device. First, there must be a sufficient amount of naled released to provide effective control of the insects in the vicinity of the device. Contrary to statements in the prior art disclosures, it has been found that release rates for naled are very much less than the release rates for DDVP. Naled has a low vapor pressure of about 2 .times. 10.sup.-4 mm. Hg. at 20.degree. C. as compared to that for DDVP of 1.2 .times. 10.sup.-2 to be thus only about 1.7% of the vapor pressure of DDVP.
It has further been found that the inclusion of an insecticide such as naled in a synthetic resin matrix in amounts sufficient to control insects for a commercially acceptable time leads to exudation of liquid insecticide (or "spew") on the surface of the device. These liquid droplets pose serious environmental and aesthetic problems as well as significantly decreasing the effective life of the device.
Parent application Ser. No. 627,671, filed Oct. 31, 1975, now U.S. Pat. No. 3,996,348, discloses and claims an improved insect-combatting device for use against houseflies, gnats, mosquitoes and the like of a shaped solid body having a porous surface capable of gradually and continually releasing naled insecticide in an amount sufficient to provide an insecticidally active concentration of said naled over a prolonged period of time, said device comprising a synthetic resinous matrix material, from about 15 to about 35 weight percent of naled and a minor amount effective to retard spewing of the insecticide of finely divided silica and at least one C.sub.14 to C.sub.20 saturated aliphatic carboxylic acid or a salt or ester thereof. The device is formed from a mixture of the synthetic resin, naled, finely divided silica particles, C.sub.14 to C.sub.20 aliphatic saturated carboxylic acid or salt or ester thereof and a surface porosity control component that is non-reactive in the mixture and has a boiling point at or below the curing temperature to produce surface openings in communication with pores in said body by vaporization of said porosity control component to provide for release of naled gas at a rate effective to control insects in the vicinity of said body, but insufficient to form as spew on the body.
Parent application Ser. No. 417,704, now U.S. Pat. No. 3,918,407 discloses and claims an improved flea control collar for a warm blooded animal comprising a strip of flexible synthetic resin material containing between about 5 and 25 wt. percent naled and having a width, thickness and length sufficient to encircle the neck of the animal with clamping means at one end of the collars for engaging a spaced collar portion to prevent loss of the collar from the neck of the wearing animal; said strip being formed from a dispersion of a synthetic resin, naled and a surface porosity control component that is non-reactive in the dispersion and has a boiling point at or below the curing temperature of said resin, said dispersion being heated to its curing temperature to produce surface openings in communication with pores in said strip by vaporization of said porosity control component to provide for release of naled gas at a rate effective to control fleas on said animal throughout a period of at least about 90 days, but insufficient to form as droplets on the strip or to be toxic to said animal.
As disclosed in these parent applications, the insect-combatting device may be formed by a variety of techniques. It is further disclosed that a further unexpected problem found with a PVC-naled composition was the tendency of the resin to decompose during the shaping process. For example, unsatisfactory results were obtained in early tests where naled was substituted for DDVP in PVC combinations employed in extrusion apparatus used for making PVC-DDVP pet collars known in the art. Burning and charring of the extrudate were found to occur during curing of the collars, and the finished collar underwent an unexplainable reduction in the naled concentration as compared with the naled concentration in the original mixture.